The present invention refers to a method for the integration of at least one additional datum in a digital data packet which is capable of being represented as a sequence of bits and comprises a first datum as well as a second datum which is capable of being unequivocally computed from said first one.
It has been found that it is often necessary within ATM installations or more generally in telecommunication installations making use of digital data packets to incorporate additional information in ATM cells, i.e. in said data packets, without violating substantially or at all the conformity of said data packets to the applicable standard in order to be able to use the currently available apparatus. A method for the integration of such information, e.g a tag or one or a plurality of flags (independently variable information units which may assume more than two different states, i.e. which are represented by more than one bit), has not been known heretofore.
In the header of ATM (Asynchronous Transfer Mode) cells, besides an address field and control field comprising a total of four bytes (octets), a fifth byte is provided which serves as a HEC (header error correction) field in order to recognize errors in the header and to correct a certain number of them.
Further known are ring-shaped transmitting networks (loops), wherein a plurality of nodes are connected in a ring by a common transmission line having a uniform transmitting direction. It is further known in such loops to recognize the packets serving for the transmission of information, e.g. address-coded packets, which cannot be delivered and therefore circulate around the loop twice or more, by means of a marker which is added in the course of the first cycle, and to eliminate them. Said marker is constituted by a bit which is specially provided for this purpose, i.e. a so-called tag, and is inverted (luring the first cycle of the packet by a node serving this purpose. In the second cycle, said node will recognize the repeated arrival of the corresponding packet by the inverted bit.
In the standardized header of ATM cells, no place is provided for a marker bit (tag) of the described kind. The use of ATM cells in ring-shaped transmitting networks is therefore subject to a concomitant restriction since these transmitting networks may very quickly become completely congested unless the repeatedly circulating packets are eliminated.